#include <sys/types.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/socket.h>
#include <netdb.h>

#define BUF_SIZE 500

        int
main(int argc, char *argv[])
{
        struct addrinfo hints;
        struct addrinfo *result, *rp;
        int sfd, s;
        struct sockaddr_storage peer_addr;
        socklen_t peer_addr_len;
        ssize_t nread;
        char buf[BUF_SIZE];

        if (argc != 2) {
                fprintf(stderr, "Usage: %s port\n", argv[0]);
                exit(EXIT_FAILURE);
        }

        memset(&hints, 0, sizeof(struct addrinfo));
        hints.ai_family = AF_UNSPEC;    /* Allow IPv4 or IPv6 */
        hints.ai_socktype = SOCK_DGRAM; /* Datagram socket */
        hints.ai_flags = AI_PASSIVE;    /* For wildcard IP address */
        hints.ai_protocol = 0;          /* Any protocol */
        hints.ai_canonname = NULL;
        hints.ai_addr = NULL;
        hints.ai_next = NULL;

        s = getaddrinfo(NULL, argv[1], &hints, &result);
        if (s != 0) {
                fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(s));
                exit(EXIT_FAILURE);
        }

        /* getaddrinfo() returns a list of address structures.
           Try each address until we successfully bind(2).
           If socket(2) (or bind(2)) fails, we (close the socket
           and) try the next address. */

        for (rp = result; rp != NULL; rp = rp->ai_next) {
                sfd = socket(rp->ai_family, rp->ai_socktype,
                                rp->ai_protocol);
                if (sfd == -1)
                        continue;

                if (bind(sfd, rp->ai_addr, rp->ai_addrlen) == 0)
                        break;                  /* Success */

                close(sfd);
        }

        if (rp == NULL) {               /* No address succeeded */
                fprintf(stderr, "Could not bind\n");
                exit(EXIT_FAILURE);
        }

        freeaddrinfo(result);           /* No longer needed */

        /* Read datagrams and echo them back to sender */

        for (;;) {
                peer_addr_len = sizeof(struct sockaddr_storage);
                nread = recvfrom(sfd, buf, BUF_SIZE, 0,
                                (struct sockaddr *) &peer_addr, &peer_addr_len);
                if (nread == -1)
                        continue;               /* Ignore failed request */

                char host[NI_MAXHOST], service[NI_MAXSERV];

                s = getnameinfo((struct sockaddr *) &peer_addr,
                                peer_addr_len, host, NI_MAXHOST,
                                service, NI_MAXSERV, NI_NUMERICSERV);
                if (s == 0)
                        printf("Received %ld bytes from %s:%s\n",
                                        (long) nread, host, service);
                else
                        fprintf(stderr, "getnameinfo: %s\n", gai_strerror(s));

                if (sendto(sfd, buf, nread, 0,
                                        (struct sockaddr *) &peer_addr,
                                        peer_addr_len) != nread)
                        fprintf(stderr, "Error sending response\n");
        }
}

